Various methods are available to remove hydrogen sulfide (H.sub.2 S) and carbon dioxide (CO.sub.2) from natural gas. One promising method which has not achieved practical success is disclosed in U.S. Pat. No. 3,767,766. In carrying out this process, the natural gas stream is contacted with a solution containing an aromatic nitrile and an alkali hydrosulfide in a substantially hydroxyl-free solvent such as N-methyl-2-pyrrolidone. The solution is regenerated by mild heating and/or pressure reduction to remove the CO.sub.2. The H.sub.2 S is removed by heating the remaining solution.
Although having an advantage over other known processes for removing H.sub.2 S and CO.sub.2 from natural gas, the process described in U.S. Pat. No. 3,767,766, herein incorporated by reference, has some significant practical problems. Experience indicates that the alkali hydrosulfide, which acts as a catalyst for the reaction of the H.sub.2 S with the nitrile, is prone to form an insoluble bicarbonate with the CO.sub.2 and trace amounts of water and to precipitate out of solution. In addition, the alkali hydrosulfide catalyzes the nitrile hydrolysis, causing a general deterioration in solution quality. The present invention is directed to the replacement of the alkali hydrosulfide with a different catalyst to overcome these undesirable side reactions.